Hi Dr. Bob. Could you please take a look at the question below and my work? I'm not sure how to get the correct answer for this question. I would greatly appreciate your help!

How many of the following molecules are polar?

BrCl3
CS2
SiF4
SO3

A) 1
B) 2
C) 3
D) 4
E) 0

The correct answer for this question is A) which is 1. However I could not find a polar molecule among the ones given.

BrCl3: the molecule has a T-shaped molecular geometry which could make it polar, but the Br-Cl electronegativity difference is 0.2 which makes it a covalent bond.

CS2: the molecule has a linear geometry and the electronegativity difference between C and S is 0, so this one is not polar either.

SiF4: the molecule has a tetrahedral molecular geometry so even though the S-iF electronegativity large and the bond is polar covalent, the bonds cancel each other out.

SO3: the molecule has a trigonal planar molecular geometry so the S-O bonds cancel each other out.

Could you please let me know which molecule is polar and why?

Your reasoning is correct for SiF4, SO3 and CS2.

BrCl3 is the polar molecule. Did you draw the Lewis structure? I can't draw it on this forum but if you try you will note that there are 28 electrons. If you place them around the Br atom, you must have two lone pairs on the central atom. The T-shape should tell you it is polar; I like to compare electronic geometries.

Thank you so much. I should've ignored the electronegativity factor.

Based on the information you provided, it seems that you have correctly analyzed the molecules and their molecular geometries. However, the correct answer for the number of polar molecules is actually 2, not 1.

The two polar molecules among the given options are BrCl3 and SO3.

BrCl3: Although the electronegativity difference between Br and Cl is small, the molecule has a T-shaped molecular geometry with an asymmetric distribution of charge. This uneven charge distribution makes BrCl3 a polar molecule.

SO3: Despite the trigonal planar molecular geometry, the electronegativity difference between S and O is significant enough to create a polar bond. Additionally, the asymmetrical arrangement of the three O atoms makes the molecule polar as well.

Therefore, the correct answer is B) 2. BrCl3 and SO3 are the two polar molecules among the given options.

Based on your analysis, you correctly identified that none of the given molecules (BrCl3, CS2, SiF4, and SO3) are polar. However, the question states that there is one polar molecule among them.

To determine the polarity of a molecule, you need to consider two factors: the molecular geometry and the electronegativity difference between the atoms forming the bonds.

For a molecule to be polar, it must have an asymmetrical shape or an uneven distribution of electron density. This means that the individual bond dipoles within the molecule do not cancel each other out.

Let's look at the given molecules in more detail:

1. BrCl3: As you correctly mentioned, it has a T-shaped molecular geometry, which could make it polar. However, the electronegativity difference between Br and Cl is only 0.2, indicating a nonpolar covalent bond. And because the molecule is symmetrical, the bond dipoles cancel, resulting in a nonpolar molecule.

2. CS2: You correctly noted that this molecule has a linear geometry, and the electronegativity difference between C and S is 0, indicating a nonpolar covalent bond. Furthermore, the molecule is symmetrical, with the sulfurs on each side of the central carbon, causing the bond dipoles to cancel out. Therefore, CS2 is a nonpolar molecule.

3. SiF4: This molecule has a tetrahedral molecular geometry, with a silicon atom at the center and four fluorine atoms surrounding it. Although the electronegativity difference is large between Si and F, the molecule is symmetrical, with the fluorines arranged at each corner of the tetrahedron. As a result, the bond dipoles cancel each other out, making SiF4 a nonpolar molecule.

4. SO3: As you correctly mentioned, SO3 has a trigonal planar molecular geometry, with the sulfur atom in the center and three oxygen atoms around it. Each S-O bond is polar due to the electronegativity difference, but because the molecule is symmetrical, the bond dipoles cancel each other out. Therefore, SO3 is a nonpolar molecule.

From your analysis, it seems there might have been a mistake or misunderstanding in the question or answer choices. It is possible that there was a typo or miscommunication. Based on your explanation, none of the given molecules are polar, and the correct answer should be E) 0 (none).